DESCRIPTION

The LWP::UserAgent is a class implementing a World-Wide Web user agent in Perl. It brings together the HTTP::Request, HTTP::Response and the LWP::Protocol classes that form the rest of the core of libwww-perl library. For simple uses this class can be used directly to dispatch WWW requests, alternatively it can be subclassed for application-specific behaviour.

In normal use the application creates a LWP::UserAgent object, and then configures it with values for timeouts, proxies, name, etc. It then creates an instance of HTTP::Request for the request that needs to be performed. This request is then passed to one of the UserAgent's request() methods, which dispatches it using the relevant protocol, and returns a HTTP::Response object.

There are convenience methods for sending the most common request types; get(), head() and post().

The basic approach of the library is to use HTTP style communication for all protocol schemes, i.e. you even receive an HTTP::Response object for gopher or ftp requests. In order to achieve even more similarity to HTTP style communications, gopher menus and file directories are converted to HTML documents.

The send_request(), simple_request() and request() methods can process the content of the response in one of three ways: in core, into a file, or into repeated calls to a subroutine. You choose which one by the kind of value passed as the second argument.

The in core variant simply stores the content in a scalar 'content' attribute of the response object and is suitable for small HTML replies that might need further parsing. This variant is used if the second argument is missing (or is undef).

The filename variant requires a scalar containing a filename as the second argument to the request method and is suitable for large WWW objects which need to be written directly to the file without requiring large amounts of memory. In this case the response object returned from the request method will have an empty content attribute. If the request fails, then the content might not be empty, and the file will be untouched.

The subroutine variant requires a reference to callback routine as the second argument to the request method and it can also take an optional chuck size as the third argument. This variant can be used to construct "pipe-lined" processing, where processing of received chuncks can begin before the complete data has arrived. The callback function is called with 3 arguments: the data received this time, a reference to the response object and a reference to the protocol object. The response object returned from the request method will have empty content. If the request fails, then the the callback routine is not called, and the response->content might not be empty.

The request can be aborted by calling die() in the callback routine. The die message will be available as the "X-Died" special response header field.

The library also allows you to use a subroutine reference as content in the request object. This subroutine should return the content (possibly in pieces) when called. It should return an empty string when there is no more content.

METHODS

The following methods are available:

$ua = LWP::UserAgent->new( %options );

This class method constructs a new LWP::UserAgent object and returns a reference to it.

Key/value pair arguments may be provided to set up the initial state of the user agent. The following options correspond to attribute methods described below:

The followings option are also accepted: If the env_proxy option is passed in an has a TRUE value, then proxy settings are read from environment variables. If the keep_alive option is passed in, then a LWP::ConnCache is set up (see conn_cache() method below). The keep_alive value is a number and is passed on as the total_capacity for the connection cache. The keep_alive option also has the effect of loading and enabling the new experimental HTTP/1.1 protocol module.

$ua->send_request($request, $arg [, $size])

This method dispatches a single WWW request on behalf of a user, and returns the response received. The request is sent off unmodified, without passing it through prepare_request().

The $request should be a reference to a HTTP::Request object with values defined for at least the method() and uri() attributes.

If $arg is a scalar it is taken as a filename where the content of the response is stored.

If $arg is a reference to a subroutine, then this routine is called as chunks of the content is received. An optional $size argument is taken as a hint for an appropriate chunk size.

If $arg is omitted, then the content is stored in the response object itself.

$ua->prepare_request($request)

This method modifies given HTTP::Request object by setting up various headers based on the attributes of the $ua. The headers affected are; User-Agent, From, Range and Cookie.

The return value is the $request object passed in.

$ua->simple_request($request, [$arg [, $size]])

This method dispatches a single WWW request on behalf of a user, and returns the response received. If differs from send_request() by automatically calling the prepare_request() method before the request is sent.

The arguments are the same as for send_request().

$ua->request($request, $arg [, $size])

Process a request, including redirects and security. This method may actually send several different simple requests.

The arguments are the same as for send_request() and simple_request().

$ua->get($url, Header => Value,...);

This is a shortcut for $ua->request(HTTP::Request::Common::GET( $url, Header => Value,... )). See HTTP::Request::Common.

$ua->post($url, \%formref, Header => Value,...);

This is a shortcut for $ua->request( HTTP::Request::Common::POST( $url, \%formref, Header => Value,... )). Note that the form reference is optional, and can be either a hashref (\%formdata or { 'key1' = 'val2', 'key2' => 'val2', ... }>) or an arrayref (\@formdata or ['key1' = 'val2', 'key2' => 'val2', ...]>). See HTTP::Request::Common.

$ua->head($url, Header => Value,...);

This is a shortcut for $ua->request( HTTP::Request::Common::HEAD( $url, Header => Value,... )). See HTTP::Request::Common.

$ua->put($url, Header => Value,...);

This is a shortcut for $ua->request( HTTP::Request::Common::PUT( $url, Header => Value,... )). See HTTP::Request::Common.

$ua->protocols_allowed( ); # to read

$ua->protocols_allowed( \@protocols ); # to set

This reads (or sets) this user-agent's list of procotols that $ua->request and $ua->simple_request will exclusively allow.

For example: $ua->protocols_allowed( [ 'http', 'https'] ); means that this user agent will allow only those protocols, and attempts to use this user-agent to access URLs with any other schemes (like "ftp://...") will result in a 500 error.

To delete the list, call: $ua->protocols_allowed(undef)

By default, an object has neither a protocols_allowed list, nor a protocols_forbidden list.

Note that having a protocols_allowed list causes any protocols_forbidden list to be ignored.

$ua->protocols_forbidden( ); # to read

$ua->protocols_forbidden( \@protocols ); # to set

This reads (or sets) this user-agent's list of procotols that $ua->request and $ua->simple_request will not allow.

For example: $ua->protocols_forbidden( [ 'file', 'mailto'] ); means that this user-agent will not allow those protocols, and attempts to use this user-agent to access URLs with those schemes will result in a 500 error.

To delete the list, call: $ua->protocols_forbidden(undef)

$ua->is_protocol_supported($scheme)

You can use this method to test whether this user-agent object supports the specified scheme. (The scheme might be a string (like 'http' or 'ftp') or it might be an URI object reference.)

Whether a scheme is supported, is determined by $ua's protocols_allowed or protocols_forbidden lists (if any), and by the capabilities of LWP. I.e., this will return TRUE only if LWP supports this protocol and it's permitted for this particular object.

$ua->requests_redirectable( ); # to read

$ua->requests_redirectable( \@requests ); # to set

This reads or sets the object's list of request names that $ua->redirect_ok(...) will allow redirection for. By default, this is ['GET', 'HEAD'], as per RFC 2068. To change to include 'POST', consider:

push @{ $ua->requests_redirectable }, 'POST';

$ua->redirect_ok($prospective_request)

This method is called by request() before it tries to follow a redirection to the request in $prospective_request. This should return a true value if this redirection is permissible.

The default implementation will return FALSE unless the method is in the object's requests_redirectable list, FALSE if the proposed redirection is to a "file://..." URL, and TRUE otherwise.

Set the user name and password to be used for a realm. It is often more useful to specialize the get_basic_credentials() method instead.

$ua->get_basic_credentials($realm, $uri, [$proxy])

This is called by request() to retrieve credentials for a Realm protected by Basic Authentication or Digest Authentication.

Should return username and password in a list. Return undef to abort the authentication resolution atempts.

This implementation simply checks a set of pre-stored member variables. Subclasses can override this method to e.g. ask the user for a username/password. An example of this can be found in lwp-request program distributed with this library.

$ua->agent([$product_id])

Get/set the product token that is used to identify the user agent on the network. The agent value is sent as the "User-Agent" header in the requests. The default is the string returned by the _agent() method (see below).

If the $product_id ends with space then the _agent string is appended to it.

The user agent string should be one or more simple product identifiers with an optional version number separated by the "/" character. Examples are:

Returns the default agent identifier. This is a string of the form "libwww-perl/#.##", where "#.##" is substitued with the version numer of this library.

$ua->from([$email_address])

Get/set the Internet e-mail address for the human user who controls the requesting user agent. The address should be machine-usable, as defined in RFC 822. The from value is send as the "From" header in the requests. Example:

Get/set the cookie jar object to use. The only requirement is that the cookie jar object must implement the extract_cookies($request) and add_cookie_header($response) methods. These methods will then be invoked by the user agent as requests are sent and responses are received. Normally this will be a HTTP::Cookies object or some subclass.

The default is to have no cookie_jar, i.e. never automatically add "Cookie" headers to the requests.

Shortcut: If a reference to a plain hash is passed in as the $cookie_jar_object, then it is replaced with an instance of HTTP::Cookies that is initalized based on the hash. This form also automatically loads the HTTP::Cookies module. It means that:

Get/set a value indicating wether we should initialize response headers from the <head> section of HTML documents. The default is TRUE. Do not turn this off, unless you know what you are doing.

$ua->max_size([$bytes])

Get/set the size limit for response content. The default is undef, which means that there is no limit. If the returned response content is only partial, because the size limit was exceeded, then a "Client-Aborted" header will be added to the response.

$ua->clone;

Returns a copy of the LWP::UserAgent object

$ua->mirror($url, $file)

Get and store a document identified by a URL, using If-Modified-Since, and checking of the Content-Length. Returns a reference to the response object.

Csh or tcsh users should use the setenv command to define these environment variables.

On systems with case-insensitive environment variables there exists a name clash between the CGI environment variables and the HTTP_PROXY environment variable normally picked up by env_proxy(). Because of this HTTP_PROXY is not honored for CGI scripts. The CGI_HTTP_PROXY environment variable can be used instead.

$ua->no_proxy($domain,...)

Do not proxy requests to the given domains. Calling no_proxy without any domains clears the list of domains. Eg:

$ua->no_proxy('localhost', 'no', ...);

SEE ALSO

See LWP for a complete overview of libwww-perl5. See lwp-request and lwp-mirror for examples of usage.

COPYRIGHT

Copyright 1995-2001 Gisle Aas.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Module Install Instructions

To install LWP::UserAgent, simply copy and paste either of the commands in to your terminal